N‐substituted poly(p‐phenylene terephthalamide)s (PPTA), such as N‐alkylated, N‐aralkylated, and N‐carboxymethylated poly(p‐phenylene terephthalamide), were synthesized from PPTA and the corresponding halides by the polymer reaction via the metalation reaction in a solution of sodium methylsulfinylcarbanion in dimethyl sulfoxide at low temperature. The introduction of various substitutional groups into the amide groups of PPTA increased their solubilities, but decreased their thermal stabilities compared with PPTA. The effects of various substitutional groups on the thermal properties and the solubilities are discussed. Liquid crystal formation was noticed for PPTA substituted with bulky groups such as 9‐anthrylmethyl group.

SynopsisThe surface of poly(p-phenylene terephthalamide) (PPTA) fiber was modified by the polymer reaction via the metalation reaction in dimethyl sulfoxide to provide the fiber surface with several functional groups such as the n-octadecyl group, carboxymethyl group, and acrylonitrile. The discontinuous fibers thus modified could be isotropically dispersed in polyethylene and ionomer. The composite of ionomer and random-in-plane oriented discontinuous PPTA fibers with the surface modified by carboxymethyl groups was remarkably improved in its mechanical properties, and the fiber efficiency factors of about 0.4 for both strength and modulus are comparable to the values in the composite of unidirectionally oriented discontinuous PPTA fibers and ionomer. The heat resistance of ionomer was also greatly improved by the presence of this surface modified PPTA fibers, even with volume fractions as low as 2.2%.

SynopsisN-octadecylated PPTA's with various molecular weights were synthesized from PPTA and noctadecyl bromide via the metalation reaction. The polymer exhibited side-chain crystallization at 314 K due to the long alkyl side chains and both crystallinity and the perfection of the crystal increase with increasing in the molecular weight. The results of IR spectra and the wide angle X-ray indicate that the polymer crystallizes in hexagonal form. The mechanical and the dynamic mechanical properties of N-octadecylated PPTA's'were measured. Two tan 6 peaks were observed in a temperature range of 310-350 K and at 260 K, respectively, which can be designated a, and cia relaxation, respectively. The concentrated solutions of N-octadecylated PPTA's in tetrahydrofuran, dichloroethane, tetrachloroethane, and bromoform showed liquid crystalline behavior of lyotropic type.

N‐grafted poly(p‐phenylene terephthalamide)s (PPTA) were synthesized from PPTA and acrylonitrile or propylene oxide via metalation in a solution of the polymer in a sodium methylsulfinylcarbanion–dimethyl sulfoxide solvent at low temperatures. The introduction of these branches into the amide groups of PPTA increased solubility but decreased thermal stability. The effects of the branches on thermal properties and solubility are discussed. The structure of the graft copolymers is described on the basis of wide‐angle x‐ray diffraction, infrared spectra, and solubility.

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A quasi‐three‐dimensional model was applied to the composite of ionomer and isotropically oriented discontinuous poly(p‐phenylene terephthalamide) (PPTA) fibers having the surface modified by carboxymethyl groups in order to predict the Young's modulus from the properties of the constituent materials over a wide temperature range. The model in which the modified PPTA fibers are dispersed in ionomer matrix in a three‐dimensional network is composed of series and parallel models. A good agreement between calculated and experimental values was eventually obtained. For comparision, the complex modulus of the composite was also evaluated by application of the Halpin‐Tsai equation modified by Nielsen. The calculated values agreed with the observed values below 240 K, whereas the calculated values above 260 K were significantly lower than the observed moduli.

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